Many radio networks use a distributed base station architecture, where a remote radio unit (RRU) is connected to a baseband processing unit (BBU) by an optical fiber, and one BBU can support multiple RRUs. In a scenario in which multiple RRUs need to be connected to a same BBU at a same station, cascading of the multiple RRUs is a common networking manner.
In the following, a data transmission mode of a wireless communications system 900 in which one BBU supports two cascaded RRUs is used as an example for description. As shown in FIG. 5, in a downlink direction, a BBU 90 receives downlink data sent by a gateway, processes the downlink data, and sends processed downlink data to an optical transceiver 93 through a common public radio interface (CPRI), where the optical transceiver is also referred to as an optical module. The optical transceiver 93 converts the processed downlink data into a first downlink optical carrier signal, and sends, through an optical fiber, the first downlink optical carrier signal to an optical transceiver 94 that corresponds to an RRU 91. The optical transceiver 94 converts the first downlink optical carrier signal into a first downlink electrical signal, and sends the first downlink electrical signal to the RRU 91. The RRU 91 selectively receives part of the first downlink electrical signal, sends the remaining signal to an optical transceiver 95. The optical transceiver 95 converts the remaining signal into a second downlink optical carrier signal, and sends the second downlink optical carrier signal to an optical transceiver 96 through an optical fiber. The optical transceiver 96 converts the second downlink optical carrier signal into a second downlink electrical signal, and sends the second downlink electrical signal to an RRU 92. In this way, the downlink data received from the gateway can be sent to a mobile terminal using the RRU 91 and the RRU 92.
In an uplink direction, the RRU 91 and the RRU 92 separately receive uplink data sent by the mobile terminal, and process the uplink data to obtain an uplink electrical signal. The RRU 92 sends an obtained first uplink electrical signal to the optical transceiver 96 that corresponds to the RRU 92. The optical transceiver 96 converts the first uplink electrical signal into a first uplink optical carrier signal, and sends, through an optical fiber, the first uplink optical carrier signal to the optical transceiver 95 that corresponds to the RRU 91. The optical transceiver 95 converts the first uplink optical carrier signal into a second uplink electrical signal, and sends the second uplink electrical signal to the RRU 91. The RRU 91 integrates the second uplink electrical signal with the uplink electrical signal obtained by the RRU 91 to obtain a third uplink electrical signal, and sends the third uplink electrical signal to the optical transceiver 94 connected to the RRU 91. The optical transceiver 94 converts the third uplink electrical signal into a second uplink optical carrier signal, and sends the second uplink optical carrier signal to the BBU 90 through an optical fiber such that the BBU 90 processes the second uplink optical carrier signal and sends a processed second uplink optical carrier signal to the gateway.
It can be seen that the RRU 91 needs to forward data sent to or from the RRU 92, and when the RRU 91 is faulty, the RRU 92 cannot work.
Therefore, the existing networking structure of a distributed base station has the following disadvantages where when an RRU (referred to as a current RRU) of cascaded RRUs is faulty, a next RRU cannot work, which reduces system reliability.